A genebank is often constrained by local environments that may be differ from ‘best practice’ defined environments.

Environment

If possible choose an environment corresponding to the original collection site conditions.

Soil type

Maize needs a large amount of macronutrients: nitrogen, potassium, and phosphorus. Maize often suffers of iron and zinc micronutrient deficiency.

Maize genotypes can differ in adaptation in the different soils and nutrient conditions.

Normal maize growth should be supported by the best possible soil conditions for cultivation to support accurate maize germplasm characterization

For example, CIMMYT Tlatizapan station has black vertisols that often limit iron availability for maize growth due to the alkaline conditions of the soil. Some inbred lines and landrace accessions present a retarded growth and even fail to flower due to these conditions.

Rainfall

500-700 mm is the optimal range in non-irrigated maize growing.

Season

Planting seasons may have a substantial effect on maize growth patterns. Even in the same locality, a winter season has slower plant growth and more days to flower than a summer season. Rain fall and temperature regimes significantly influence maize growth pattern. In addition, data on leaf diseases, ear quality, ear rots and plant lodging can be affected by wind, edaphic and biotic environmental factors in the different growing seasons.

Characterization data should be associated with the season in which the maize germplasm accessions are characterized.

Plot size

When characterization is performed at the same time of regeneration, use 16 rows, 5 m long, with 256 plants per plot for landrace accessions.

If an evaluation trial is conducted for characterization purposes only, plant one accession in two 5 m long rows and in 2 replications.

Half-size plots can be used for inbred lines.

The distance between rows should be 75 cm.

Adjust the plot size according to maturity and plant height, to facilitate normal plant growth.

Sampling area/border area

Use at least one border row encircling characterization trials, to avoid border effects.

Plant density

For tall and late tropical maize landraces, plant two seeds per hill to establish 16 plants per row after thinning.

Adjust density according to maturity and plant height.

Aged seeds from the genebank storage may have a reduced rate of field germination.

Single seeds per hill may be planted if seed accessions have good seed germination.

Replications

Normally un-replicated entries are planted for the regeneration of accessions.

For characterization trials of accessions, two replications are often used for a more rigorous statistical analysis.

Standard check cultivars

In replicated characterization trials, standard check cultivars can be landrace accessions and single cross hybrids or commercial hybrids.

Several common check cultivars should be included across different characterization trials.